Science Buddies: "Ask an Expert"

Hi,

I'm basing my science project on the Crazy Crystal Creations which I found on sciencebuddies.com. Can an expert answer my question as the 'professional contact' required by my teacher?

If you're growing a borax crystal in a containter which is closed, once the entire container is filled with crystals will it continue to grow and break the container open or will it stop growing? Is there some condition which will cause it to stop before it completely filled up the container? Is there a material which would push the container open?

If you cannot be my professional contact, can you send me in the right direction to find someone who can act as a professional contact?

Thanks
JDRocks

You need to do some of your own research (searching of articles) on crystal growth. Fundamentally, crystal growth occurs by depositing solid material from either a liquid or a gas onto an existing crystal "seed". The "material" forming the crystal is NOT created, just its physical state.

If you "seal" the container completely, then you will alter the behavior of the crystal growth process and change the thermodynamics. If the formation of the crystal is exothermic, then heat will have to be transfered out of the container for crystal growth to continue. If the formation of the crystal is endothermic, then heat will have to transfered into the container for crystal growth to continue.

It takes borax in liquid or gas phase to grow borax crystals. If you seal a container with some amount of borax in various states, you will only have that amount of borax inside the sealed container at a later time. This means there is a limit to how much borax crystal that can form. If the borax in crystaline state takes up more volume than in the liquid or gas phase, then it maybe possible to split the container; however, that would depend on what happens to the other liquids and gasses.

Hi JDRocks,

I hope your teacher will let you use this forum as "professional contact". I study crystallography, so I basically study crystals for a living. So growing a crystal from solution is what is referred to as a phase change. You can imagine all of the borax atoms floating around in the water and then once they reach the right conditions (usually temperature or concentration), they precipitate or fall out of the solution as a solid crystal. When you have a phase change, like going from a solid to a liquid, you usually have a change in volume. When you have all three phases (solid, liquid, or gas) at the same pressure, then the gas occupies a larger volume than a liquid or a solid. Most substances contract when they change from a liquid to a solid (except for water which actually expands).

So if you are growing the crystals in a container that is closed, you actually won't be able to fill the entire box with crystals unless you continue to add more borax. The reason is that the crystals form because the solution is supersaturated. So the crystals will precipitate until it reaches a point where it is in equilibrium (so the same number of crystals are forming and dissolving at the same time). If you keep adding borax then you continue to drive the solution towards the solid phase... but then you don't actually have a closed container. So the crystals will stop growing. One compound that would cause the container to break when you form crystals is just plain old water. When you crystallize water (or freeze it) then all of the liquid actually forms crystals and as I mentioned above the volume expands, which would then break the container.

I hope this helps. Good luck with your experiments

tzforbes